LED illumination, as a novel technique for environment-friendly illumination, has been developed rapidly in the past years. A constant-current driver circuit has now been presented so as to meet the requirements on the characteristics of the LEDs. Main technical indices for measuring LED constant-current driving include efficiency, power factor, linear adjustment rate, constant-current accuracy and various protection functions. The power factor, as an important technical index for a power system, is used to measure the efficiency of an electrical device. The lower the power factor, the larger the reactive power used by a circuit for alternating magnetic-field conversion. Hence, the utilization rate of the device is reduced, a line power loss is increased and a harmonic pollution at an input end becomes more serious.
An existing LED driver circuit includes a ringing choke converter (RCC) circuit which consists of analog elements, so it is greatly superior in cost. However, the power factor of the RCC circuit is not high, and its constant-current effect is bad. In addition, it is difficult for the conversion efficiency of the RCC circuit with an isolation structure to be up to more than 80%. Due to these defects, it is difficult for the RCC circuit to take its advantages in the LED driver circuit.